Engineering materials for electronic assemblies

Abstract

As a soldering material for use in an electronic assembly, the soldering material comprises soldering layers; and a core layer comprising a core material, wherein the core layer is interposed between the soldering layers, and wherein the thermal conductivity of the core material is greater than the thermal conductivity of the solder.

Description

Technology Field

[0001] The present invention relates to a soldering material for use in electronic assemblies.

[0002] There are two major challenges associated with the packaging and assembly of high-power electronic devices, such as IGBTs, MOSFETs, high-power LEDs, high-power microprocessors, and other large-area devices that generate a significant amount of heat during normal operation. The first is how to ensure the efficient dissipation of heat generated to maintain normal operating temperatures. The second is how to reduce shear stress caused by a mismatch in the coefficient of thermal expansion (CTE) between materials of adjacent layers attached by solder or other adhesive materials.

[0003] FIG. 1 illustrates an assembly of a typical electronic device (1) comprising a device (2) connected to a substrate (4) via an interconnect (3) (Level I). The substrate (4) is connected to a printed circuit board (PCB) (6) via an interconnect (5) (Level II). The PCB (6) is connected to a heat sink (8) via an interconnect (7) (Level III). The most important interconnects for high-power electronic devices are the interconnects that connect the device / die to the substrate, the substrate to the printed circuit board (PCB), and the PCB to the heat sink, namely 3, 5, and 7 of FIG. 1. Such interconnects are located in the heat dissipation path. Therefore, high thermal conductivity of the interconnect materials is required. Semiconductor die, substrate, and PCB materials have different CTEs, thereby causing stress at the interface during high-temperature operation. To minimize that stress, designers generally increase the interface thickness of the interconnects, but this ultimately increases the thermal resistance of the interface.

[0004] Solder is one of the most common interconnect materials used in the electronics industry. The thermal conductivity of most solders is less than 65 W / mK. It would be advantageous to use interconnect materials with higher thermal conductivity to aid in heat dissipation. Another problem with thick solder interconnects is that during the reflow process, when the solder is in the liquid phase, the die or substrate floats on the liquid material before the solder cools below its cooling temperature. This results in movement of the die / substrate in all directions (so-called "tilt"), which poses another concern regarding device performance and reliability. Controlling this die movement is a difficult challenge.

[0005] The present invention aims to solve at least some of the problems associated with the prior art or at least provide a commercially acceptable alternative solution thereto.

[0006] In a first embodiment, the present invention provides a soldering material for use in an electronic assembly, and the soldering material is,

[0007] Soldering layers; and

[0008] It includes a core layer containing a core material, and

[0009] The core layer is interposed between the solder layers, and

[0010] Here,

[0011] The thermal conductivity of the core material is greater than the thermal conductivity of the solder.

[0012] Each aspect or embodiment as defined in this specification may be combined with any other aspect(s) or embodiment(s) unless otherwise clearly indicated. In particular, any feature indicated as preferred or advantageous may be combined with any other feature indicated as preferred or advantageous.

[0013] The inventors have surprisingly discovered that when such soldering material is used to connect components of electronic devices operating at elevated temperatures, it may be possible to reduce stress caused by a mismatch in the CTE values ​​of the connected components. Without being bound by theory, it is assumed that the presence of a core material acts to "thicken" the joint between the connected components, thereby reducing stress. Advantageously, such stress reduction can be provided without significantly reducing heat dissipation from the connected parts. Without being bound by theory, this is assumed to be because the thermal conductivity of the core material is greater than the thermal conductivity of the solder. In other words, by using a core material having a thermal conductivity greater than that of the solder, it is possible to thicken the joint to reduce thermal stress without reducing heat dissipation. As a result, high-power electronic devices such as IGBTs, MOSFETs, high-power LEDs, high-power microprocessors, or other large-area devices that generate significant heat during normal operation (where the components are connected using soldering materials) can exhibit improved performance and / or reliability. Such performance and reliability can be improved at elevated temperatures and / or during switching on and off.

[0014] Joints or interconnects formed using soldering materials can have better thermo-mechanical reliability compared to typical Pb-free solders such as SnCu, SAC, SnAg, and SnBi.

[0015] The term “electronic assembly” as used herein includes, for example, an assembly of electronic packages and devices, and may include, for example, the attachment of a device or die to a substrate, a substrate to a printed circuit board, or a printed circuit board to a heat sink.

[0016] The term "soldering" as used in this specification includes fusible metals or metal alloys having a melting point in the range of 90 to 400°C.

[0017] The soldering material comprises soldering layers and a core layer. The soldering material is essentially composed of soldering layers and a core layer, or may be composed of these. "Consisting essentially of" means that the soldering material may include other non-specific components, provided that other non-specific components do not materially affect the properties of the soldering material.

[0018] The soldering material typically comprises two soldering layers, but may comprise more than two soldering layers. The soldering layers may be formed from the same solder or different solders. Typically, the soldering layers are formed from the same solder, or at least solders having liquidus temperatures that differ by similar reflow temperatures, i.e., 20°C or less, typically 10°C or less, more typically 5°C or less.

[0019] The solder and core are in the form of layers. Such layers may typically be in the form of sheets having two opposing surfaces (main surfaces) that have a surface area significantly larger than the other surfaces. The solder layers may have the same size and shape or different sizes and / or shapes. The core layer may have a size and shape similar to one or more of the solder layers or different sizes and / or shapes.

[0020] The core layer includes a core material. The core layer is essentially made of the core material or may be made of these.

[0021] A core layer is interposed between solder layers. Typically, the solder layers will substantially cover at least two opposing surfaces of the core layer, namely, the entire surface of the main (i.e., the surface with the largest surface area). The core layer can be completely encapsulated within the solder so that no core material is exposed. In such a situation, the first solder sheet is considered to cover the main surface of the sheet, and the second solder layer is considered to cover the opposing main surface of the sheet, wherein the two solder layers "overhang" the main surfaces to cover the remaining surfaces of the core layer. Alternatively, the core layer may be covered by solder layers only on some of the surfaces, typically only on the two opposing surfaces, and more typically only on the main surfaces.

[0022] Solder layers are typically in direct contact with the core layer. Solder layers are typically outer layers.

[0023] The thermal conductivity of the core material is greater than that of the solder. Typically, such thermal conductivity is measured by a nano-flash transient measurement technique.

[0024] The core material preferably has a thermal conductivity of 65 W / mK or higher, preferably greater than 65 W / mK, more preferably greater than 70 W / mK, and even more preferably greater than 75 W / mK. The core material may have a thermal conductivity of less than 600 W / mK. Such thermal conductivity can be measured by nano-flash transient measurement techniques. Since typical solders used in electronic assemblies have a thermal conductivity of less than 65 W / mK, the presence of a core material having a higher thermal conductivity increases the overall thermal conductivity of the solder material.

[0025] The melting point of the core material is preferably greater than the reflow temperature of the solder. For example, the core material may have a melting temperature that is at least 50°C higher than the reflow temperature of the solder, typically at least 75°C higher, and more typically at least 100°C higher. The term "reflow temperature" is used herein to refer to the temperature at which the solid mass of the solder definitely melts (as opposed to merely softening). If cooled below this temperature, the solder will not flow. If heated again above that temperature, the solder will flow again, i.e., "reflow." By having a core material with a melting temperature higher than the reflow temperature of the solder, the thickness of the joint / interconnection can be increased without a substantial increase in die / package movement and / or tilt, which results in the die / package floating on top of the liquid solder when the solder is in a liquid state. This can improve the performance or reliability of electronic devices having components connected using the solder material.

[0026] The thickness of the core layer is preferably 100 to 500 μm, more preferably 200 to 400 μm, and even more preferably 150 to 300 μm. Such a thickness may be particularly suitable for reducing stress caused by CTE mismatch of components without excessively increasing the size of the electronic device. Larger thicknesses may increase thermal resistance. Relatively higher thicknesses may result in higher resistance but may result in lower lateral stress.

[0027] The thickness of each solder layer is preferably 25 to 150 μm, more preferably 50 to 100 μm, even more preferably greater than 50 to 99 μm, even more preferably 55 to 95 μm, and still even more preferably 60 to 90 μm. In a preferred embodiment, the thickness of each solder layer is greater than 50 μm to 150 μm. In another preferred embodiment, the thickness of each solder layer is 55 μm to 150 μm. Such thicknesses may be particularly suitable for providing adequate adhesion between components without significantly reducing the overall thermal conductivity of the solder material or excessively increasing the size of the device. Lower thicknesses may result in higher lateral stress during high-temperature operation of temperature cycling.

[0028] The thickness of the core and solder layers can be selected as desired by the package design and to achieve the desired thickness of the interconnects.

[0029] The core material preferably comprises metals and / or alloys (or is made of these, or is essentially made of these). Metals and metal alloys can provide sufficient electrical conductivity to provide a high level of electrical connection between components joined by the soldering material.

[0030] The core material preferably comprises one or more of copper, silver, nickel, molybdenum, beryllium, cobalt, iron, copper-tungsten alloy, nickel-silver alloy, copper-zinc alloy and copper-nickel-zinc alloy, more preferably one or more of copper and silver (or consists of these, or essentially consists of these). Such materials can provide an advantageous combination of high electrical conductivity and high thermal conductivity.

[0031] The CTE of the core material will have an effect on stress at interfaces. This stress can be reduced by selecting an appropriate core material. For example, the CTE of nickel is 13 ppm / K, while the CTE of copper is 17 ppm / K, and the CTE of CuW alloys depends on the composition and can be customized to meet device design needs.

[0032] The core material is preferably at least 1 x 10 at 20°C. 5 S / m, more preferably at least 1 x 10 6 S / m, more preferably at least 1 x 10 7 S / m, more preferably at least 4 x 10 7 S / m, still, even more preferably at least 5 x 10 7 It has an electrical conductivity of S / m. Such electrical conductivity can provide a high level of electrical connection between components joined by a soldering material.

[0033] Soldering is preferably lead-free. This means that no lead is intentionally added. Therefore, the lead content is zero or below the levels of accidental impurities. Lead-free soldering can be advantageous in terms of health issues and regulatory requirements.

[0034] The solder is preferably made of In, SnIn alloy (e.g., 5 to 58% Sn, 42 to 95% In), SnBi alloy (e.g., 42 to 60% Sn, 40 to 58% Bi), BiIn alloy (e.g., 5 to 67% Bi, 33 to 95% In), AgIn alloy (e.g., 1 to 5% Ag, 95 to 99% In, e.g., 3% Ag, 97% In), SnAg alloy (e.g., 90 to 97.5% Sn, 2.5 to 10% Ag), SnCu alloy (e.g., 99.3 to 99.6% Sn, 0.4 to 0.7% Cu), InGa alloy (e.g., 99.3 to 99.5% In, 0.5 to 0.7% Ga), SnBiAgCu alloy (e.g., 50% Sn, 47%) Bi, 1% Ag, 2% Cu), SnBiZn alloy (e.g., 65.5% Sn, 31.5% Bi, 3% Zn), SnInAg alloy (e.g., 77.2% Sn, 20% In, 2.8% Ag), SnBiAgCuIn alloy (e.g., 82.3% Sn, 2.2% Bi, 3% Ag, 0.5% Cu, 12% In), SnZn alloy (e.g., 91% Sn, 9% Zn), SnCuInGa alloy (e.g., 92.8% Sn, 0.7% Cu, 6% In, 0.5% Ga), SnCuAg alloy (e.g., 95.5% Sn, 3.8% Ag, 0.7% Cu), SnAgSb alloy (e.g., 95% Sn, 3.5% Ag, 1.5% Sb), SnSb alloy (e.g. For example, it includes one or more of 95% Sn, 5% Sb), Innolot alloy (Sn-Ag 3.7Cu 0.65Bi 3.0Sb 1.43Ni 0.15), and SnCuSb alloy (e.g., 4 to 95% Sn, 1 to 2% Cu, 4% Sb). % values ​​refer to weight %. The alloys may contain the mentioned elements along with any unavoidable impurities. Such alloys may be particularly suitable for connecting components of electrical devices.

[0035] In a preferred example, the core material contains copper, and the solder contains Sn-20In-2Ag alloy.

[0036] In a preferred embodiment, the thickness of the core layer is 150 to 300 μm, the thickness of each solder layer is greater than 50 to 100 μm, and the core material comprises one or more of copper and silver. In such an embodiment, the thickness of each solder layer is preferably 55 to 100 μm. Such a solder material can, in particular, reduce stress caused by a mismatch in the CTE values ​​of connected components without significantly reducing heat dissipation from the connected parts.

[0037] The core layer preferably comprises two or more core sublayers separated by one or more additional soldering layers, and the two or more core sublayers are formed of a core material, wherein the core material of one sublayer has a different coefficient of thermal expansion than the core material of another sublayer. This may result in the soldering material having a different coefficient of thermal expansion on one side than on the other. This can be beneficial when connecting components having different coefficients of thermal expansion and can reduce stress caused by different coefficients of thermal expansion at high temperatures. In such cases, a component having a higher coefficient of thermal expansion can be connected to the side of the soldering material having the core sublayer having the higher coefficient of thermal expansion, and a component having a lower coefficient of thermal expansion can be connected to the side of the soldering material having the core sublayer having the lower coefficient of thermal expansion.

[0038] The additional solder layer includes a soldering material. The soldering material of the additional solder layer may be the same as the soldering material of the solder layer. Alternatively, the soldering material of the additional solder layer may be different from the soldering material of the solder layer.

[0039] The core material of one core sublayer is preferably different from the core material of another core sublayer.

[0040] The soldering material preferably comprises two sublayers. In a preferred embodiment of such an arrangement, the core material of one core sublayer preferably comprises copper, and the core material of the other core sublayer preferably comprises nickel. Such metals may result in the soldering material exhibiting a favorable change in the coefficient of thermal expansion across its thickness.

[0041] The soldering material preferably comprises three sublayers. In such a case, the coefficient of thermal expansion of the core material of the core sublayer preferably increases across the thickness of the soldering material, that is, in a direction perpendicular to the plane of the core layer. In a preferred embodiment of such an arrangement, the three sublayers comprise one inner sublayer and two outer sublayers, the core material of one core sublayer comprises copper, the core material of another core sublayer comprises nickel, and the core material of the other core sublayer comprises a copper-tungsten alloy. In another preferred embodiment, the core material of one core sublayer comprises silver, the core material of another core sublayer comprises nickel, and the core material of the other core sublayer comprises molybdenum. Such metals may result in the soldering material exhibiting a favorable change in the coefficient of thermal expansion across its thickness.

[0042] The core sublayers may have different thicknesses, or the core sublayers may have the same thickness. The core sublayer may preferably have a thickness of 10 to 80 μm, more preferably 20 to 60 μm, and even more preferably 25 to 50 μm.

[0043] The additional solder layer may have the same thickness as the aforementioned solder layer, or may have a different thickness from the aforementioned solder layer.

[0044] In a preferred embodiment,

[0045] The soldering material is not in the form of a cuboid having a length, width, and thickness with a thickness perpendicular to the plane of the core layer and a length of 10 mm and a width of 10 mm;

[0046] The thickness of the core layer is not 0.2 mm, 0.3 mm, or 0.4 mm;

[0047] The soldering layer does not have a thickness of 0.05 or 0.1 mm, or / or;

[0048] The soldering material does not contain Sn20%In2%Ag and / or;

[0049] The core material does not contain copper.

[0050] In a more preferred embodiment,

[0051] The soldering material is not in the form of a cube having length, width, and thickness, with a thickness perpendicular to the plane of the core layer and a length of 10 mm and a width of 10 mm;

[0052] The thickness of the core layer is not 0.2 mm, 0.3 mm, or 0.4 mm;

[0053] The soldering layers do not each have a thickness of 0.05 or 0.1 mm;

[0054] The soldering material does not contain Sn20%In2%Ag;

[0055] The core material does not contain copper.

[0056] The soldering material is preferably in the form of a foil, strip, film, ribbon, or preform, more preferably a preform. Such forms may be particularly suitable for connecting components of electronic devices and / or may exhibit advantageous handling properties.

[0057] In a preferred embodiment, the core is completely coated with solder. In other words, the core is completely surrounded by solder, and no part of the core is exposed. In this case, no part of the core material is exposed to air or other operating environments. This design may be desirable for core materials that tend to oxidize when exposed to humidity and / or oxygen, such as, for example, Cu or Ni.

[0058] In an alternative preferred embodiment, the core is soldered only on two opposing surfaces, that is, typically on the two largest opposing surfaces (main surfaces). This design can be relatively easy for high-volume manufacturing because large sheets or ribbons can be soldered so that the preform can be cut by a high-speed stamping process.

[0059] The soldering material preferably has an effective thermal conductivity greater than 65 W / mK, more preferably greater than 80 W / mK, even more preferably greater than 100 W / mK, and still even more preferably greater than 130 W / mK. "Effective thermal conductivity" means the total thermal conductivity of the soldering material, including both the solder (which has lower thermal conductivity) and the core (which has higher thermal conductivity). Such effective thermal conductivity can improve heat dissipation from the soldering material.

[0060] A first aspect of the present invention relates to a soldering material. The term "soldering material" may be synonymous with the term "multilayer structure." Additionally, the term "soldering layers" is synonymous with the term "two or more soldering layers." Additionally, to avoid any doubt, the soldering layers comprise a soldering material. The soldering layers are typically outer layers.

[0061] Accordingly, a first aspect of the present invention is alternatively expressed as a multilayer material for use in an electronic assembly, and the multilayer material is,

[0062] Two or more (e.g., outer) solder layers - each solder contains solder material later -; and

[0063] It includes a core layer comprising a core material, wherein the core layer is interposed between two or more solder layers, and

[0064] Here,

[0065] The thermal conductivity of the core material is greater than the thermal conductivity of the soldering material.

[0066] In a further aspect, the present invention provides a multilayer structure for use in an electronic assembly, wherein the multilayer structure is,

[0067] Two outer soldering layers - each outer soldering layer contains soldering material -; and

[0068] It includes a core layer interposed between two outer solder layers, and

[0069] Here,

[0070] The core layer comprises two outer core sublayers and optionally one or more central core sublayers;

[0071] Two core sublayers, and central core layers if present, are separated from each other by one or more soldering layers;

[0072] The outer core sublayers and the inner core sublayers include a core material;

[0073] The core material of one outer core sublayer has a different coefficient of thermal expansion than the core material of another outer core sublayer;

[0074] The thermal conductivity of core materials is greater than that of soldering materials.

[0075] The advantages and desirable features of the first embodiment apply equally to this embodiment.

[0076] The core preferably comprises at least one central core sublayer, and the coefficients of thermal expansion of the core materials of the outer and inner core sublayers increase across the thickness of the core. As discussed above in relation to the first embodiment, this can be beneficial when connecting components having different coefficients of thermal expansion and can reduce stress caused by different coefficients of thermal expansion at high temperatures.

[0077] In a further embodiment, the present invention provides a solder joint comprising the solder material described herein or the multilayer structure described herein. To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to this embodiment. Such a joint may exhibit an advantageous combination of low stress and high heat dissipation caused by the CTE mismatch of the bonded components. Accordingly, an electronic device comprising such a joint may exhibit improved performance and reliability compared to conventional electronic devices. The thickness of the solder joint corresponds to the sum of the thicknesses of the core layer and the solder layers. Typically, the thickness does not change during reflow.

[0078] In a further embodiment, the present invention provides an interconnect comprising the soldering material described herein or the multilayer structure described herein. To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to this embodiment. Such an interconnect may exhibit an advantageous combination of low stress and high heat dissipation caused by the CTE mismatch of the bonded components. Accordingly, an electronic device comprising such an interconnect may exhibit improved performance and reliability compared to conventional electronic devices.

[0079] In a further embodiment, the present invention provides an electronic device comprising a soldering material, a multilayer structure, a solder joint, or an interconnection as described herein. To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to this embodiment. Such a device may exhibit improved performance and reliability compared to conventional electronic devices.

[0080] In a further embodiment, the present invention provides an IGBT, MOSFET, LED, or microprocessor comprising the soldering material, multilayer structure, solder joint, or interconnection described herein. To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to this embodiment. Such devices may exhibit improved performance and reliability compared to conventional electronic devices.

[0081] In a further embodiment, the present invention provides for the use of the soldering materials or multilayer structures described herein in a soldering method selected from Surface Mount Technology (SMT) soldering, die-attachment soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, and thermosonic soldering. To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to this embodiment. The soldering materials and multilayer structures described herein are particularly suitable for such applications.

[0082] In additional embodiments, the present invention provides for the use of the soldering materials or multilayer structures described herein for die attachment (Level I), substrate attachment (Level II), or package-heatsink attachment (Level III). To avoid any doubt, the advantages and preferred features of the first embodiment are equally applicable to these embodiments. The soldering materials and multilayer structures described herein are particularly suitable for such applications.

[0083] In a further aspect, the present invention provides a method for forming a solder joint, the method being

[0084] The step of providing a soldering material described herein or a multilayer structure described herein in the vicinity of two or more workpieces to be joined, and

[0085] It includes the step of heating the soldering material to form a soldered joint.

[0086] To eliminate any doubt, the advantages and desirable features of the first embodiment apply equally to this embodiment. The resulting joint may exhibit a favorable combination of low stress and high heat dissipation caused by the CTE mismatch of the joined components. Accordingly, an electronic device comprising such a joint may exhibit improved performance and reliability compared to conventional electronic devices.

[0087] Two or more workpieces to be joined are preferably,

[0088] Device or die and substrate, or

[0089] Substrates and printed circuit boards (PCBs), or

[0090] Includes printed circuit boards and heatsinks.

[0091] Such workpieces are particularly suitable for joining with soldering materials, as they are required to have high heat dissipation and it is advantageous for them to exhibit low stress resulting from CTE mismatch.

[0092] In a further embodiment, the present invention provides a method for manufacturing a soldering material or a multilayer structure described herein, the method being

[0093] Step of providing two or more solder layers,

[0094] A step of providing a layer of core material, and

[0095] It includes the step of laminating solder layers on both sides of a layer of core material.

[0096] To eliminate any doubt, the advantages and desirable features of the first embodiment apply equally to this embodiment. Depending on the soldering and core materials as well as the processing conditions, there is a reduction in the thickness of the structure after lamination. The reduction factor must be taken into account to achieve target dimensions.

[0097] The layer of the core material is preferably in the form of a ribbon and / or the soldering layer is in the form of a ribbon.

[0098] Ribbons are preferably provided by casting, extrusion, or drawing.

[0099] The layers are preferably laminated in a co-drawing process, preferably a high-pressure co-drawing process.

[0100] The laminated layers are preferably diced and / or stamped.

[0101] In a further embodiment, the present invention provides a method for manufacturing a soldering material or a multilayer structure described herein, the method being

[0102] A step of providing a layer of core material, and

[0103] It includes the step of coating the core material with solder.

[0104] The surface of the layer of the core material is preferably cleaned before it is coated with solder. This can result in stronger adhesion between the core and the solder, thereby reducing the occurrence of delamination and the resulting loss of reliability of the device including the joint formed using the solder material.

[0105] The step of coating the core material with solder preferably includes the step of bringing the core material into contact with a molten solder bath, for example, by immersing the core material in a molten solder bath.

[0106] Various process parameters, such as soldering bath temperature and ribbon speed through the bath, can be changed to control the soldering coating thickness. Brief explanation of the drawing

[0107] The present invention will now be described in connection with the following non-limiting drawings. Figure 1 shows a schematic diagram of an assembly of a typical electronic device. FIG. 2 illustrates a schematic cross-sectional view of alternative arrangements of soldering materials according to the present invention. FIG. 3 illustrates a schematic cross-sectional view of a soldering material according to the present invention. FIG. 4 illustrates a schematic cross-sectional view of a soldering material according to the present invention. Figure 5 shows a microscopic image of a cross-section of a soldering material according to the present invention. FIG. 2 illustrates cross-sectional views of two types of soldering materials according to the present invention. The soldering materials include a core layer (9) interposed between soldering layers (10). The soldering material shown in the top drawing has soldering only on the top and bottom faces. No soldering exists on the faces. The other soldering material has soldering on all faces of the core. FIGS. 3 and FIGS. 4 illustrate cross-sectional views of two types of soldering materials according to the present invention. In the soldering material of FIG. 3, the core layer (9) comprises two core sublayers (11) separated by an additional soldering layer (12). The two core sublayers (11) are formed from a core material. The core material of the upper sublayer has a different coefficient of thermal expansion than the core material of the lower sublayer. In a preferred embodiment, the core material of the upper core sublayer is nickel, and the core material of the lower core sublayer is nickel. As a result, the CTE decreases from the top to the bottom. In the soldering material of FIG. 4, the core layer (9) comprises three core sublayers (11) separated by an additional soldering layer (12). The three core sublayers (11) are formed from a core material. The core material of the upper sublayer has a different coefficient of thermal expansion than the core materials of the middle sublayer and the lower sublayer. The coefficients of thermal expansion of the core materials of the core sublayers may increase or decrease across the thickness of the soldering material. In a preferred embodiment, the core material of the top core sublayer is molybdenum, the core material of the middle core sublayer is nickel, and the core material of the bottom core sublayer is silver. As a result, the CTE decreases from the top to the bottom. In another preferred embodiment, the core material of the top core sublayer is a copper-tungsten alloy, the core material of the middle core sublayer is nickel, and the core material of the bottom core sublayer is copper. As a result, the CTE increases from the top to the bottom. Specific details for implementing the invention

[0108] The present invention will now be described in connection with the following non-limiting embodiments.

[0109] Example 1

[0110] A soldering material (preform) was prepared by a high-pressure lamination process. Figure 5 shows a microscopic image of a cross-section of the preform. The central core has a thickness of 300 μm and is formed of copper. The soldering on both sides is Sn20%In2%Ag. The soldering thickness varies from 50 to 100 μm. The effective thermal conductivity of this sample is approximately 130 W / mK, measured by a nano-flash transient measurement technique.

[0111] Example 2

[0112] Multiple preforms were prepared in a manner similar to Example 1, but with varying thicknesses of the core (Keff = 400 W / mK) and solder layers (Keff = 54 W / mK). The thermal performance of the preforms was evaluated. Table 1 shows the estimated thermal resistances and equivalent thermal conductivity. The thermal resistance of the hick interfaces is significantly lower compared to solder alone (the equivalent Keff is significantly higher).

[0113] [Table 2]

[0114]

[0115] The present invention will now be further described with reference to the following numbered items:

[0116] 1. As a soldering material,

[0117] A core including a core material; and

[0118] A soldering material comprising a solder that at least partially coats the core.

[0119] 2. Regarding Item 1,

[0120] Soldering material is a soldering material intended for use in electronic assemblies.

[0121] 3. In Item 1 or Item 2,

[0122] The core is a soldering material in the form of layers.

[0123] 4. Regarding Item 3,

[0124] A soldering material having a core layer thickness of 100 to 500 μm, preferably 200 to 400 μm, more preferably 150 to 300 μm.

[0125] 5. In Item 3 or Item 4,

[0126] Soldering is in the form of layers, and the core is a soldering material interposed between two soldering layers.

[0127] 6. Regarding Item 6,

[0128] A soldering material having a soldering layer thickness of 25 to 150 μm, preferably 50 to 100 μm.

[0129] 7. In any one of Items 1 through 6,

[0130] Soldering material is a soldering material in the form of foil, strip, film, ribbon, or preform.

[0131] 8. In any one of Items 1 through 7,

[0132] A soldering material whose melting point is greater than the reflow temperature of the solder.

[0133] 9. In any one of Items 1 through 8,

[0134] A soldering material in which the thermal conductivity of the core material is greater than the thermal conductivity of the solder.

[0135] 10. Regarding Item 9,

[0136] A soldering material having a thermal conductivity of 65 W / mK or higher, preferably greater than 65 W / mK, more preferably greater than 70 W / mK, and even more preferably greater than 75 W / mK.

[0137] 11. In any one of Items 1 through 10,

[0138] The core material is a soldering material comprising metal and / or alloy.

[0139] 12. In any one of Items 1 through 11,

[0140] A soldering material comprising one or more of the following: a core material, silver, nickel, molybdenum, beryllium, cobalt, iron, copper-tungsten alloy, nickel-silver alloy, copper-zinc alloy, and copper-nickel-zinc alloy.

[0141] 13. In any one of Items 1 through 12,

[0142] Solder is a lead-free soldering material.

[0143] 14. In any one of Items 1 through 13,

[0144] Soldering is made of In, SnIn alloy (e.g., 5 to 58% Sn, 42 to 95% In), SnBi alloy (e.g., 42 to 60% Sn, 40 to 58% Bi), BiIn alloy (e.g., 5 to 67% Bi, 33 to 95% In), AgIn alloy (e.g., 3% Ag, 97% In), SnAg alloy (e.g., 90 to 97.5% Sn, 2.5 to 10% Ag), SnCu alloy (e.g., 99.3 to 99.6% Sn, 0.4 to 0.7% Cu), InGa alloy (e.g., 99.3 to 99.5% In, 0.5 to 0.7% Ga), SnBiAgCu alloy (e.g., 50% Sn, 47% Bi, 1% Ag, 2% Cu), SnBiZn alloy (e.g., 65.5% Sn, 31.5% Bi, 3% Zn), SnInAg alloy (e.g., 77.2% Sn, 20% In, 2.8% Ag), SnBiAgCuIn alloy (e.g., 82.3% Sn, 2.2% Bi, 3% Ag, 0.5% Cu, 12% In), SnZn alloy (e.g., 91% Sn, 9% Zn), SnCuInGa alloy (e.g., 92.8% Sn, 0.7% Cu, 6% In, 0.5% Ga), SnCuAg alloy (e.g., 95.5% Sn, 3.8% Ag, 0.7% Cu), SnAgSb alloy (e.g., 95% Sn, 3.5% Ag, 1.5% Sb), and SnCuSb alloy (e.g., 4 to 95% Sn, 1 to 2% Cu, Soldering material containing one or more of 4% Sb.

[0145] 15. In any one of Items 1 through 14,

[0146] A soldering material in which the core material contains copper and the solder contains Sn-20In-2Ag alloy.

[0147] 16. In any one of Items 1 through 15,

[0148] A soldering material in which the core and solder are in the form of layers, and the solder layers are coated on both sides of the core layer.

[0149] 17. Regarding Item 16,

[0150] A soldering material having a core layer thickness of 100 to 500 μm, preferably 200 to 400 μm, more preferably 150 to 300 μm.

[0151] 18. In Item 16 or Item 17,

[0152] A soldering material having a soldering layer thickness of 25 to 150 μm, preferably 50 to 100 μm.

[0153] 19. In any one of Items 1 through 18,

[0154] A soldering material in which the core is completely coated with solder.

[0155] 20. In any one of Items 1 through 19,

[0156] A soldering material having an effective thermal conductivity of greater than 65 W / mK, preferably greater than 80 W / mK, more preferably greater than 100 W / mK, and even more preferably greater than 130 W / mK.

[0157] 21. Use of a soldering material of any one of items 1 to 20 in a soldering method selected from surface mount technology soldering, die attachment soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, and thermo-sonic soldering.

[0158] 22. Use of any one of items 1 through 20 of the soldering material for die attachment (Level I), substrate attachment (Level II), or package heatsink attachment (Level III).

[0159] 23. An interconnection comprising a soldering material of any one of items 1 to 20.

[0160] 24. An IGBT, MOSFET, LED, or microprocessor comprising a soldering material of any one of items 1 through 20, or an interconnect of item 23.

[0161] 25. A method for forming a solder joint,

[0162] A step of providing a soldering material of any one of items 1 to 20 in the vicinity of two or more workpieces to be joined, and

[0163] A method comprising the step of heating a soldering material to form a soldered joint.

[0164] 26. A method for manufacturing a soldering material of any one of items 1 to 20,

[0165] Step of providing two or more solder layers,

[0166] A step of providing a layer of core material, and

[0167] A method comprising the step of laminating soldering layers on both sides of a layer of core material.

[0168] 27. In Item 26,

[0169] A method in which a layer of core material is in the form of a ribbon and / or a soldering layer is in the form of a ribbon.

[0170] 28. Regarding Item 27,

[0171] Ribbons are provided by casting, extrusion, or drawing methods.

[0172] 29. In any one of items 26 through 28,

[0173] A method in which layers are laminated in a co-drawing process, preferably a high-pressure co-drawing process.

[0174] 30. In any one of items 26 through 29,

[0175] A method in which laminated layers are diced and / or stamped.

[0176] 31. A method for manufacturing a soldering material of any one of items 1 to 20, wherein

[0177] A step of providing a layer of core material, and

[0178] A method comprising the step of coating a core material with solder.

[0179] 32. Regarding Item 31,

[0180] A method in which the surface of a layer of core material is cleaned before the core material is coated with solder.

[0181] 33. In Item 31 or Item 33,

[0182] A method comprising the step of coating a core material with solder, wherein the core material is passed through a molten solder bath.

[0183] 34. In any one of Items 1 through 20,

[0184] Soldering material in the form of a preform.

[0185] 35. Regarding Item 34,

[0186] A preform is a soldering material that reduces stress at the interface of adjacent materials having soldering by increasing the CTE from top to bottom.

[0187] 36. Regarding Item 34,

[0188] A preform is a soldering material that reduces stress at the interface of adjacent materials having soldering by decreasing the CTE from top to bottom.

[0189] 37. In any one of items 34 through 36,

[0190] Preform is a soldering material that can be used for Level I, Level II, or Level III interconnects.

[0191] 38. In any one of items 34 through 37,

[0192] Preforms are soldering materials that can be used for packaging and assembly of IGBTs, MOSFETs, LEDs, microprocessors, and other electronic devices.

[0193] 39. In any one of items 34 through 38,

[0194] A preform is a soldering material that can be used for assembling multi-chip modules having components with different heat generation rates and components of different sizes.

[0195] 40. In any one of items 34 through 39,

[0196] A soldering material that can be used for assembling multi-chip modules having components of different thicknesses, and the preform thickness is selected to be adjusted with respect to the component thickness.

[0197] The foregoing detailed description is provided for illustrative and illustrative purposes only and is not intended to limit the scope of the appended claims. Many variations of the currently preferred embodiments illustrated in this specification will be apparent to those skilled in the art and are within the scope of the appended claims and their equivalents.

Claims

Claim 1 A soldering material for use in an electronic assembly, comprising: soldering layers; and a core layer comprising a core material, wherein the core layer is interposed between the soldering layers, wherein the thermal conductivity of the core material is greater than the thermal conductivity of the solder, and the core layer comprises two or more core sublayers separated by one or more additional soldering layers, wherein the two or more core sublayers are formed of a core material, wherein the core material of one sublayer has a different coefficient of thermal expansion than the core material of another sublayer, and the thickness of each soldering layer is 25 to 150 μm. Claim 2 In claim 1, the core material is a soldering material having a thermal conductivity of 65 W / mK or more. Claim 3 A soldering material according to claim 1, wherein the melting point of the core material is greater than the reflow temperature of the solder. Claim 4 A soldering material according to claim 1, wherein the thickness of the core layer is 100 to 500 μm. Claim 5 A soldering material according to claim 1, wherein the thickness of each soldering layer is 50 to 100 μm. Claim 6 In claim 1, the core material is a soldering material comprising a metal and / or an alloy. Claim 7 In claim 1, the core material comprises one or more of copper, silver, nickel, molybdenum, beryllium, cobalt, iron, copper-tungsten alloy, nickel-silver alloy, copper-zinc alloy, and copper-nickel-zinc alloy, a soldering material. Claim 8 In claim 1, the solder is a lead-free soldering material. Claim 9 In claim 1, the soldering material comprises one or more of In, SnIn alloy, SnBi alloy, BiIn alloy, AgIn alloy, SnAg alloy, SnCu alloy, InGa alloy, SnBiAgCu alloy, SnBiZn alloy, SnInAg alloy, SnBiAgCuIn alloy, SnZn alloy, SnCuInGa alloy, SnCuAg alloy, SnAgSb alloy, SnSb alloy, Innolot alloy, and SnCuSb alloy. Claim 10 In claim 1, the core material comprises copper, and the solder comprises Sn-20In-2Ag alloy, the soldering material. Claim 11 In claim 1, the thickness of the core layer is 150 to 300 μm, the thickness of each solder layer is greater than 50 to 100 μm, and the core material comprises one or more of copper and silver, a soldering material. Claim 12 A soldering material according to claim 11, wherein the thickness of each soldering layer is 55 to 100 μm. Claim 13 In claim 1, the core material of one core sublayer is a soldering material different from the core material of the other core sublayer. Claim 14 A soldering material comprising two core sublayers in claim 1. Claim 15 In claim 14, the core material of one core sublayer comprises copper, and the core material of the other core sublayer comprises nickel, a soldering material. Claim 16 A soldering material comprising three core sublayers in claim 1. Claim 17 In paragraph 16, the coefficients of thermal expansion of the core materials of the core sublayers increase across the thickness of the soldering material. Claim 18 In claim 16, the above three sublayers comprise one inner sublayer and two outer sublayers, and the core material of one core sublayer comprises copper, the core material of another core sublayer comprises nickel, and the core material of another core sublayer comprises a copper-tungsten alloy, a soldering material. Claim 19 A soldering material according to claim 16, wherein the core material of one core sublayer comprises silver, the core material of another core sublayer comprises nickel, and the core material of another core sublayer comprises molybdenum. Claim 20 In claim 1, the core sublayers are soldering materials having different thicknesses. Claim 21 In claim 1, the soldering material is not in the form of a cuboid having the length, the width, and the thickness, wherein the thickness is perpendicular to the plane of the core layer and the length is 10 mm and the width is 10 mm; the thickness of the core layer is not 0.2 mm, 0.3 mm, or 0.4 mm; the soldering layer does not have a thickness of 0.05 or 0.1 mm, respectively; the soldering material does not contain Sn20%In2%Ag; and the core material does not contain copper. Claim 22 A soldering material in the form of a foil, strip, film, ribbon, or preform according to claim 1. Claim 23 In claim 1, the core is a soldering material that is completely coated with the solder. Claim 24 In claim 1, the soldering material is a soldering material having an effective thermal conductivity of more than 65 W / mK. Claim 25 A multilayer structure for use in an electronic assembly, comprising: two outer soldering layers—each outer soldering layer comprising a soldering material—; and a core layer interposed between the two outer soldering layers, wherein the core layer comprises two outer core sublayers and optionally one or more central core sublayers; the two core sublayers and, if present, the central core layers are separated from one another by one or more soldering layers; the outer core sublayers and the inner core sublayers comprise a core material; the core material of one outer core sublayer has a different coefficient of thermal expansion than the core material of another outer core sublayer; the thermal conductivity of the core materials is greater than the thermal conductivity of the soldering materials; and the thickness of each soldering layer is 25 to 150 μm. Claim 26 In paragraph 25, the core comprises at least one central core sublayer, and the coefficient of thermal expansion of the core materials of the outer and inner core sublayers increases across the thickness of the core, forming a multilayer structure. Claim 27 A solder joint comprising a soldering material of any one of claims 1 to 24 or a multilayer structure of claim 25 or 26. Claim 28 An interconnection comprising a soldering material of any one of claims 1 to 24 or a multilayer structure of claim 25 or 26. Claim 29 An IGBT comprising a soldering material of any one of claims 1 to 24, or a multilayer structure of claim 25 or 26. Claim 30 A soldering material used in a soldering method selected from Surface Mount Technology (SMT) soldering, die attachment soldering, thermal interface soldering, hand soldering, laser and RF induction soldering, and thermosonic soldering, in any one of claims 1 to 24. Claim 31 A soldering material for use in die attachment (Level I), substrate attachment (Level II), or package heatsink attachment (Level III), in any one of claims 1 to 24. Claim 32 A method for forming a solder joint, comprising the steps of: providing a soldering material according to any one of claims 1 to 24 in the vicinity of two or more workpieces to be joined; and heating the soldering material to form a soldered joint. Claim 33 In claim 32, the two or more works to be joined comprise a device or die and a substrate, or a substrate and a printed circuit board (PCB), or a printed circuit board and a heatsink. Claim 34 In paragraph 32, the method wherein the two or more works have different heat generation rates and / or different sizes when in use. Claim 35 A method according to claim 32, wherein the two or more workpieces to be joined comprise at least three workpieces, said workpieces have different thicknesses, said soldering materials are used to join the different workpieces, and said soldering materials are adjusted to reduce a mismatch in the coefficient of thermal expansion between said workpieces. Claim 36 In paragraph 32, the method wherein the solder joint is formed during the assembly of a multi-chip module. Claim 37 In claim 32, the core layer comprises two or more core sublayers separated by one or more additional soldering layers, the two or more core sublayers are formed of a core material, the core material of one sublayer has a different coefficient of thermal expansion than the core material of another sublayer, and the sublayers are arranged such that the coefficient of thermal expansion of the core material of the sublayers increases across the thickness of the soldering material to provide a surface having a higher coefficient of thermal expansion and a surface having a lower coefficient of thermal expansion; the two or more workpieces to be joined have contact materials having different coefficients of thermal expansion; the soldering material is disposed between the two or more workpieces, and the workpiece having the contact material having the lower coefficient of thermal expansion contacts the surface having the lower coefficient of thermal expansion and the workpiece having the contact material having the higher coefficient of thermal expansion contacts the surface having the higher coefficient of thermal expansion. Claim 38 A method for manufacturing a soldering material of any one of claims 1 to 24 or a multilayer structure of claim 25 or 26, comprising the steps of providing two or more soldering layers, providing a layer of a core material, and laminating the soldering layers on both sides of the layer of the core material. Claim 39 In paragraph 38, the method wherein the layer of the core material is in the form of a ribbon and / or the soldering layer is in the form of a ribbon. Claim 40 In paragraph 39, the method wherein the ribbon is provided by casting, extrusion, or drawing. Claim 41 In paragraph 38, the above layers are laminated in a co-drawing process. Claim 42 In paragraph 38, the above-mentioned laminated layers are diced and / or stamped in a method. Claim 43 A method according to claim 38, further comprising the steps of: providing an additional layer of core material; laminating the additional layer of core material onto a soldering layer; providing an additional soldering layer; and laminating the additional soldering layer onto the additional layer of core material. Claim 44 A method according to claim 43, further comprising the steps of: providing another additional layer of a core material; laminating the other additional layer of the core material onto a soldering layer or an additional soldering layer; providing another additional soldering layer; and laminating the additional soldering layer onto the other additional layer of the core material. Claim 45 A method for manufacturing a soldering material of any one of claims 1 to 24 or a multilayer structure of claim 25 or 26, comprising the steps of providing a layer of a core material and coating the core material with solder. Claim 46 In paragraph 45, a method wherein the surface of the layer of the core material is cleaned before the core material is coated with the solder. Claim 47 In paragraph 45, the step of coating the core material with soldering comprises the step of bringing the core material into contact with a molten solder bath. Claim 48 delete

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